Field strength meter



March 20, 1951 R. w. GILBERT FIELD STRENGTH METER Filed oQt. 30, 194e INVENTOR.

Patented Mar. 20, 1951 FIELD. STRENGTH METER Roswell-i W1" Gilbert; Montclair,v Nl J assignor t'o Weston Electrical- Instrument: Corporation Newark, Nin Ji,

a; corporation oi-Av Newi J ersey Application October 30, 1946.-,SeriaLNm 706,576

4:1 Claims'.

This invention relates.; to measuring instruments and.` in., particular to those; for indicating the presence and approximate magnitude. of electfricalel'ds; especially in the high and ultra high frequency ranges.

The general objlet ofthe invention is to provide a new and improvedj construction for an instrument of," the class. described` which. is economicalito, manufacturepompact, light in Weight and whichis equally adaptableforfhand usek or for wall mounting.

Another object is to provide av 'eld". strength instrument comprising an indicator component and a probe component,`r the, two parts being readily detachable, for replacement` of] either part or; for. insertion of a cable between them to permitthe meter component to belocated somewhat remote from the probe.

Another object is toprovideanovel construction for,- a. probe, used in. investigatingv electric field phenomena..

These and other objects. and advantages of the, invention will become moreV` apparent from the,` following` detailed description, of a preferred embodiment when considered. with the accompanyingVV drawings in which;

Fig.. l; is. a. front viewot the, instrument the vprobe component being shown detached, from the. indicator and. mostly nsection. to. show. de.- tailsA of.4 its. construction;

Fig. 2' is a side elevation of the meter component? Fig. 3 is an enlarged fragmentary perspective view of the upperu portion of'a support rod in the probe and` Fig. 4 is a schematic circuit. diagram of the instrument; t

Referring now to Fig. 1,V the eld strength indicator component is comprisedA of au support member I preferably made fromA materialj-v having agoodinsulating characteristic s uch as a1 plastic. It. i'nclud'es an upper housing section 2 that; containsv a sensitive current indicating devicev such as4 a microammeter 3 ofthe permanent magnet, movable coil' type, the pointer 4 being rotated over the scale 5 asa. function of the magnitude of the current passed through the instrument coihandalower hand portion 6, provided with a rather long andV vertically extending slot l. As shown in Fig: 2; thereanface Ia of the support I is. flat; sof: as. to;` permit.l it.` to; be` attached toY and liel against; a.: wall. or; other` support by;` l'rleanS.V 0f a. bolt 8K whicltA exten-def through;V the; slot: 1f.. a washer '9 being placed between the head of; the bolt and the front face of the handle so as to clamp the device tightly against the wall.

A threadedL sleeve l0 of electrically conductive material with a center conducting pin I'.I extends upwardly throughA thel top wall'. of` the casing 2 and these are connected inside of the casing.l by leads (not shown) to the two terminals on. the microammeter` 3 leading to the coil.

The probe component is generally indicated by reference numeral I5 and is comprised of. a cylindrical member I-B of electrically conductive material that is bored axially at. Ifl for receiving and supporting the. lower endl of a cylindrical post I8 of insulating material.` The-lower end, of the bore through member I6 isenlarged at. [Sto the diameter of sleeve, I0. andisinternally threaded for threaded engagement with this.y sleeve.`

The lower end of post I8 is provided with; an axial bore 2 D for theinsertionof amulti-ngered socket; 2ll wthingwhichg the pin I i isz receivedz as the probe I5 and casingvarecoupled togetlfier;`

Theupper end laof thepost I8 as shown` in Fig. 3 includes a pair of oppositely disposedarcuately shapedV recessesA 22 that extend longitudinally for supporting a pair of crystal rectiers 23. and 24, knowncommercially as the 1N type.

A round` plate 25' of` conductive; materialA is supported on the top end face of post I So This plate is electrically connected tothe upper terminals ofthe two; rectifiers 23.` and 24. by means of leads 25 which may be soldered to slugs; of solder 21. embedded in. the top of: plate: 25,.

A double coil R. chokeis wound on post I8 andconsistsof' two coils 28l andv 29 wound; inthe same relative direction. The upper end; offv coll 28A is connected tothe lowerend of rectifier 23and its lowery endl is connected to. the socket. 251'.' by means of a radial bore 3I1in post I8.which ccnnects with the axial' bore 20. The upper endl of coilv 29vis connected to thel lower1 end of' rectier 24 and its lower end connected'to-the conductive body member IB suchY as by solder-ingV at'32.

As seen in Fig. 4, these electrical connections are such that the' upper'ends ofA thechoke coils are connected'v to the rectiiiersv while the lower ends are connected to thetermin-als on microammeter'3`; Itis also to loe-noted in Fig: 4;'that-the recti'ers 23" and 24 are so connected ina loop circuit including" the coils 28,` 29, plate 25 and the rectiers as to establish a unidirectional: iiow of current through the.` microammetery 3.

The. distributed capacity between coils 28j.' and 29 is indicated in Fig. 4" by plates 33 drawn in by broken lines. A separate by-pass condenser 34 between these coils may insomecases, be desirable.` The latter has, not been, shown in the other views.

The probe component I5 is preferably encased Operation The manner of operation of the device should now be apparent. If hand use is intended, the instrument (with the indicator casing and probe l5 coupled together) may, for example, be brought into proximity with a conductor 3l to be investigated, substantially as shown in Fig. 1. In known manner, the high frequency eld associated with the conductor induces a high frequency potential gradient along the elements within the probe through the space capacitance existing between the probe and the conductor. The resultant high frequency current flows through the rectifier elements 23 and 24 producing a direct current component which will be indicated on the microammeter. The scale of the microammeter 3 is not intended to be graduated in any absolute systei of notation since the instrument is good only for obtaining reasonably accurate approximations of the absolute values of the fields.

If it is desired to locate the meter at a somewhat remote distance from the probe l5, they may be detached from each other and electrically coupled by the insertion of a two wire cable (not shown) of the desired length with suitable end connections :for screw threaded attachment to the sleeve I6 and body member i6.

If the instrument is attached to a wall or other support, the slot and bolt connection in the handle 6 will permit tine adjustment of the probe i5 with respect to the conductor 3l so as to locate the probe at any desired point in the highV frequency field.

The field strength measuring instrument which has been described has wide application and numerous uses will be found for it' by those working in this art. To note a few, the following may be listed:

'riod standing waves on circuit leads or transmission lines).

d. Detection of R.F. in power rectifier plate supplies (the usual cause of arc-back troubles).

e. Shielding leaks and location of radiation leaks in high frequency heating installations.

f. Transmission line balancing and matching.

g. Phasing of antenna arrays.

Cil

h. Resonance indication in simple frequency meters.

z'. Routine checking of small mobile transmitters by indicating R.F. voltage in antenna (small aircraft, police cars, ctc).

In conclusion, it will of course be-understood that while in accordance with the patent statutes I have shown and described a preferred embodiment of the invention, various changes in the construction and arrangement ofv parts may be made without departing from the spirit and scope ofthe invention as defined in the appended claims.

I claim:

1. In an instrument of the class described; a probe adapted for capacitative coupling to a measured circuit, said probe comprising an elongated double coil choke, a pair of rectifiers supported at the upper end of said choke, and a conductive plate supported above said rectifiers and which constitutes one electrode of the coupling, each said rectifier being connected between said plate and the upper end of one of said choke coils; a support of insulating material for said probe, said support including an upper housing and a lower handle portion; a current indicating device Within said housing; and means detachably connecting said probe to said housing, the lower ends of said choke coils being electrically connected to said current indicating device through said detachable connecting means.

2. An instrument as defined in claim 1 wherein the handle portion of said support is provided with an elongated vertical slot for receiving a bolt whereby said instrument may be adjustably attrical fields, said probe comprising an insulating post, the lower portion of said post being cylindrical and the upper portion recessed at opposite sides, a rectiiier disposed in each recess, a conductive plate above said rectifiers, an elongated double wound choke on the cylindrical portion of said post, a cylindrical support member of conductive material having an upper axial bore for receiving the lower end of said post and a lower threaded portion, and a socket disposed within an axial recess at the lower end of said post, said rectiiiers being connected respectively between said plate and the upper ends of said choke coils, the lower ends of said coils being connected respectively to said socket and to said support member.

4. In an instrument of the class described, a probe adapted for capacitative coupling to a measured circuit, said probe comprising an elongated choke coil, rectier means supported at the upper end of said coil, a conductive plate constituting one electrode of said coupling supported above said rectier means, and electrical connections from said plate to said coil through s aid rectier means, an insulating member supporting said probe, a current indicating device carried by said insulating member, and electrical connections between said coil and current indicating device.

RoswELL W. GiLBERT.

REFERENCES CITED The following references are of record-in the file of this patent:

UNITED STATES PATENTS OTHER REFERENCES Publication, A Portable Electrometer for the Measurement of Electrostatic Charges; Bulgin, Journalof Scientific Instruments, vol. 22, Aug. 1945. 

